1. Field of the Invention
The present invention relates to a technique of detecting a change in a voice recognition function and processing a voice signal to be recognized such that the voice signal to be recognized is adapted to the change.
2. Description of the Related Art
Terminal devices of in-vehicle information technology instruments, mobile phones, or the like in which is built a voice recognition function have been developed in order for a user to operate such a terminal device by his/her voice. Recently, due to the development of data communication technology, a voice recognition method with higher accuracy has been widely available, in which a voice uttered by a user is inputted into a terminal device and is transmitted as a voice data to a voice recognition server via a network, and an abundant calculation resource of the voice recognition server is used for a voice recognition. The voice recognition always involves a risk of false recognition owing to effects of indistinct utterance of a user, background noise, or the like. If a user continues to operate an instrument for voice recognition without realizing a false recognition, user's convenience is greatly damaged. Thus, for example, Japanese Laid-Open Patent Application, Publication No. 2005-091611 (see, for example, paragraph 0012) discloses a technique in which, based on an amount of a noise contained in an uttered voice and information on a cause of occurrence of the noise, only an uttered voice which is determined to be voice-recognizable is targeted for a voice recognition.
As described above, more and more voice recognition servers are operated as a generally available service in recent years. In many of those cases, an entity which provides a service for a terminal device handled by a user is different from an entity which operates a voice recognition server. Thus, in some cases, if a voice recognition function of the voice recognition server is changed, the user may not notice the change. Further, even if a provider of a service is at the same time an operator performs the service, because an internal state (for example, an amount of processing load) of a voice recognition server varies from moment to moment, it may be difficult to completely and continuously monitor a change in voice recognition performance. In this case, if a service of a voice recognition function is continuously provided to a user and, for example, voice recognition performance of a voice recognition server used becomes lower for some reason, a reduction in the voice recognition performance cannot be detected. As a result, the user may be provided with a low-quality voice recognition service.
If a voice data transmitted from a terminal device to a voice recognition server is subjected to some data manipulation processing in order to obtain better voice recognition performance, a change in the voice recognition performance of the voice recognition server may reduce effects of the data manipulation processing or may lower the voice recognition performance compared to a case in which the data manipulation processing is not performing.
In the light of the described above, the present invention has been made in an attempt to provide a voice recognition service with a stable quality.